The present invention relates to a variable displacement type compressor. More particularly, the present invention relates to a method for controlling displacement in the variable displacement type compressor.
In a typical variable displacement type compressor that introduces and compresses a refrigerant through reciprocating movement of a piston and raises the pressure of the refrigerant to be discharged, to reduce its weight, the variable displacement type compressor includes a hollow piston. The hollow piston is generally manufactured by connecting two members. When the hollow piston is employed, even at high-speed operation of the variable displacement type compressor, inertial force generated by the movement of the piston is relatively restrained and strength of the piston is relatively ensured. Also, the hollow piston effectively prevents hunting caused by unstable piston strokes and improves displacement control even at the high-speed operation.
However, compared to a solid piston, the hollow piston is more costly to manufacture since two members are required to manufacture the hollow piston. In spite of its lower cost, if the solid piston is applied to a compressor, the weight of the piston increases and the solid piston may negatively influence the strength of the piston itself and the displacement control, especially at high-speed operation. Thus, the weight of the piston is an element that determines the inertia force caused by the movement of the piston. The hollow piston increases the reliability of the compressor itself, such as the strength of the piston itself and the displacement control, but the difficulty of lowering the manufacturing cost still remains. Whereas, the solid piston lowers the manufacturing cost, but increasing the reliability of the compressor itself remains difficult.
Japanese Unexamined Patent Publication No 2001-90667 discloses such a variable displacement type compressor that controls its displacement control valve so as to decrease the amount of discharged refrigerant as the rotational speed of a vehicle engine becomes high. The above mentioned variable displacement type compressor effectively controls the amount of discharged refrigerant based on a variation of the inertia force of the piston especially at the high-speed operation.
However, the compressor that controls amount of discharged refrigerant based on the rotational speed has the following problem. For instance, even when control of the amount of discharged refrigerant is not required in spite of the high rotational speed for the vehicle engine, the control of the amount of the discharge refrigerant is performed. Even when the compressor is relatively at a low running state, controlling the amount of discharged refrigerant is performed and thus the amount of discharged refrigerant decreases.
The present invention is directed to a variable displacement type compressor that accurately controls the displacement of discharged refrigerant by taking an operating state of the compressor into consideration.
According to the present invention, a variable displacement type compressor circulates a refrigerant in an air conditioning circuit. The compressor has a compression mechanism and a displacement controller. The compression mechanism compresses and discharges an amount of the refrigerant at a discharge pressure. The displacement controller controls the discharge amount of the refrigerant of the compressor based upon displacement. The displacement controller further includes a normal control means and a protective control means. The normal control means controls the displacement based on a cooling load. The protective control means controlling the displacement based on a value in connection with a rotational speed of the compressor and the actual operating information on the compressor which is determined by a value of an actual discharge amount and a reference value of the discharge amount.
The present invention also provides a method for controlling a displacement of a variable displacement type compressor. The method includes detecting a cooling load, controlling a discharge amount of a refrigerant based on the cooling load, detecting a value in connection with a rotational speed of the compressor, calculating the value of the actual discharge amount of the refrigerant, calculating the reference value of the discharge amount of the refrigerant, determining the actual operating information based on the value of the actual discharge amount and the reference value of the discharge amount, and further controlling the actual discharge amount based on the value in connection with the rotational speed and the actual operating information.